The "Pay and get" system is getting boring. Let's think of something new. Hmm...how about something like this?
Part 1 - The sennin that teaches forbidden jutsu!
As you were walking along the forest path, you suddenly spot a suspicious-looking character lurking in the shadow of the bushes. You grab your kunai and decides to jump on him!
~~~Fight~~~
You have encountered The Infamous Scroll-Stealing-Sennin, Muku Muku which lunges at you with Forbidden Jutsu!
He is tough. So tough that normal academy students will just die a horrible death, genin will hardly be able to make it out alive, chunnin might make it with some luck, jounin will have to be very skilled at fighting to survive this one...
Once you beat him, he will let you choose one of the many color-coded scroll he has. You wouldn't know what it is until you have chosen a scroll.
Part 2 - Learning the forbidden jutsu!
As you walk along the forest path, you spot Sennin Muku Muku peeking at the ladies who are having fun by the waterfall. "Are all sennin like that?!" you thought to yourself as you tab him on his shoulder. He jump up in surprise then notice it was just you. "So you have come to practice the forbidden jutsu that you have chosen right?"
> Yes, let's get started.
> No, I have come here to peek at the ladies as well.
If you chose "yes" a battle will start.
~~~Fight~~~
You have encountered The Forbidden Jutsu Sennin, Muku Muku which lunges at you with (the jutsu that you have choosen)!
The forbidden jutsu of your choice (Level 1) will be added to you list of jutsu once you have successfully beaten him.
Part 3 - Mastering the forbidden jutsu!
You will have to fight him over & over again each time you meet him in the forest. After each fight, the option "Am I getting any better?" will pop up. Click it, if it says "No" then better luck next time, but if it's a "yes" you gain Level 2, 3 and so on.
Forbidden Jutsu!
1) It shares the same jutsu use points (chakra usage) as your normal jutsu.
example: Kage Bunshin no Jutsu (1) / Forbidden Jutsu Level 1 (1) and you only have 1 jutsu point. If you use either jutsu, your jutsu point will go to 0 the moment you pick one so you either use Kage Bunshin or Forbidden Jutsu, not both.
2) Unlike normal jutsu, it has 5 levels. Each level uses more and more chakra. With the forbidden jutsu, you will have a skill to use at 4 jutsu points.
3) It wouldn't go away even after a "dragon kill".
4) You cannot learn more than 1 forbidden jutsu. If you want to learn from another scroll, you will have to forget this one by asking Sennin Muku Muku to wipe it from your memory and he will let you chose another scroll.